William Herschel Discovered Spiral Galaxy NGC 673 Sept. 4, 1786

Summary: Uranus discoverer William Herschel discovered spiral galaxy NGC 673 Sept. 4, 1786, five years five-plus months after discovering Uranus March 13, 1781.

NGC 673 appears as II-589 in Uranus discoverer Sir William Herschel’s list of “II. Second Class. Faint Nebulae” discoveries; the spiral galaxy in Aries was the second of two galaxies that he discovered Sep. 4, 1786: Sloan Digital Sky Survey (SDSS), CC BY 4.0 International, via Wikimedia Commons

Uranus discoverer William Herschel discovered spiral galaxy NGC 673 Sept. 4, 1786, five years five-plus months after his March 13, 1781, discovery of Uranus, the solar system’s seventh planet.

German-British astronomer and composer Sir Frederick William Herschel (Nov. 15, 1738-Aug. 25, 1822) made his discovery of NGC 673 at his last residence, known as Observatory House, on Windsor Road in Slough, Royal County of Berkshire, south east England. The instrument that he used for the discovery was his 20-foot, long-focus Newtonian reflector telescope. The model had an 18.7 inch-aperture.

Sir William’s discovery appears as number 589 under “II. Second Class. Faint Nebulae” in his Catalogue of a Second Thousand of New Nebulae and Clusters of Stars, published in 1789. He arranged his discoveries of new nebulae and star clusters into eight classes. The first class concerned “Bright nebulae.” Classes three through eight comprised, respectively, “Very faint nebulae”; “Planetary nebulae”; “Very large nebulae”; “Very compressed and rich clusters of stars”; “Pretty much compressed clusters of large or small stars”; “Coarsely scattered clusters of stars.”

In his observations, Sir William identified “the star, or other object” that “is either preceding or following” the nebula. Object II-589 precedes “24 (ξ) Ariet,” a binary star in Aries the Ram constellation.

Sir William used both Bayer and Flamsteed stellar designations in his identification of the “determining star.” German celestial cartographer Johann Bayer (1572-March 7, 1625) designated stars with a Greek or Latin letter followed by the genitive form of the parent constellation’s Latin name. The Bayer designation for II-580’s “determining star” is ξ Arietis (Xi Arietis; ξ Ari (Xi Ari). A number followed by the Latin genitive of the parent constellation characterizes the stellar designation system devised by the United Kingdom’s first Astronomer Royal, John Flamsteed (Aug. 19, 1646-Dec. 31, 1719). Xi Arietis bears the Flamsteed designation of 24 Arietis.

According to Sir William’s observations, object II-589 precedes the binary star by a sidereal time of 36 minutes 21 seconds. His calculations place object II-589l at 0 degrees 50 minutes north of the star system.

Sir William made two observations of II-589. He described II-589 as “F. pL. E. b.ſ.M. 2’ ſp. cBſt.” His abbreviated description translates as: “Faint. Pretty large. Extended. Brighter suddenly in the middle. 2’ south preceding. Extremely bright star.”

Sir William’s faint nebula appears as NGC 673 in the New General Catalogue, published in 1888 by Danish-Irish astronomer John Louis Emil Dreyer (Feb. 13, 1852-Sept. 14, 1926). Dreyer’s catalogue assigned NGC (New General Catalog) numbers to discoveries and observations by Sir William; his son, Sir John Frederick William Herschel, 1st Baronet (March 7, 1792-May 11, 1871); his sister, Caroline Herschel (March 16, 1750-Jan. 9, 1848); and other observational astronomers.

NGC 673 is located in Aries the Ram constellation. The galaxy’s equatorial coordinates are right ascension of 01 hour 48 minutes 22.440 seconds, declination of plus 11 degrees 31 minutes 16.71 seconds (epoch J2000.0), according to NASA/IPAC Extragalactic Database (NED).

The NED Database classifies NGC 673 with a galaxy morphology of SAB(s)c. The classification denotes an intermediate spiral galaxy with weakly barred, ringless spirals and loosely wound arms. NGC 673 is a 13th-magnitude spiral galaxy, according to the online Celestial Atlas of NGC Objects maintained by Courtney Seligman, Professor Emeritus of Astronomy at California’s Long Beach City College.

Sir William’s II-589 was the second of two galaxies that he discovered Sept. 4, 1786. The first galaxy, II-588, is known now as NGC 665 and lies in the neighboring constellation of Pisces the Fishes.

The takeaway for NGC 673, discovered Sept. 4, 1786, by German-British astronomer and composer Sir William Herschel, is that spiral galaxy NGC 673 is the second of two same-day galactic discoveries by the discoverer of Uranus.

NGC 665 appears as II-588 in Uranus discoverer Sir William Herschel’s list of “II. Second Class. Faint Nebulae” discoveries; the lenticular galaxy in Pisces was the first of two same-day galactic discoveries that he made Sep. 4, 1786: Sloan Digital Sky Survey (SDSS), CC BY 4.0 International, via Wikimedia Commons

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

NGC 673 appears as II-589 in Uranus discoverer Sir William Herschel’s list of “II. Second Class. Faint Nebulae” discoveries; the spiral galaxy in Aries was the second of two galaxies that he discovered Sep. 4, 1786: Sloan Digital Sky Survey (SDSS), CC BY 4.0 International, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:NGC673_-_SDSS_DR14.png

NGC 665 appears as II-588 in Uranus discoverer Sir William Herschel’s list of “II. Second Class. Faint Nebulae” discoveries; the lenticular galaxy in Pisces was the first of two same-day galactic discoveries that he made Sep. 4, 1786: Sloan Digital Sky Survey (SDSS), CC BY 4.0 International, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:NGC665_-_SDSS_DR14.png

For further information:

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